(1.) Field of the Invention
The present invention relates to a pinion shift starter for internal combustion engines in which the torque from the starter motor shaft is transmitted to the flywheel ring gear through a reciprocable pinion which is moved forward into engagement with the flywheel ring gear by an engaging sleeve which is coupled to the motor shaft by a solenoid switch.
(2.) Description of the Prior Art
There have been developed various types of starters for small general purpose internal combustion engines, such as Bendix type starters and pinion shift starters as disclosed in Japanese laid-open patent specification No. 58-15659.
In a Bendix type starter, the coupling means pushes the pinion into engagement with the ring gear on the flywheel while it, driven by the starter, rotates in inertia, so that the starter can turn the engine. When the engine begins to rotate faster than the starter, the coupling means, urged by the return spring, is pulled back to home position disengaging the pinion from the flywheel ring gear. A serious problem with those Bendix type starters is that disengagement between the starter and engine, which is effected when the difference in speed of their rotation has reached a certain point, can take place before the engine is started to the sufficient speed for firing. Another problem is the great noise the starters develop when the pinion is brought into engagement with the flywheel ring gear since the engagement takes place with the pinion in rotation.
In a pinion shift starter, a magnetic field set up by the solenoid when the starter switch is pressed brings the coupling sleeve into engagement with the starter motor shaft, and pushes the coupling sleeve against the pinion which, in turns, moves into engagement with the ring gear on the flywheel. As long as the solenoid is held down in energized position, disengagement between the starter motor and engine will not take place so that the latter can be started until firing.
However, in those conventional pinion shift starters, since the designs require the starter motor and associated devices, such as a solenoid switch, to be installed in compact space at the end of the crankcase on the opposite side of the crankcase end wall, a hole has to be drilled in the crankcase end wall to permit the pinion to enter the crankcase for engagement with the ring gear on the flywheel. One of the problems with the prior art starters of this type is that this hole has given unwanted freedom for a foreign matter such as dust and debris to enter the chamber in which the starter is housed.
Various device have so far been proposed to eliminate this problem. One such a device is a dust hood adapted to enclose the flywheel, as illustrated in FIG. 2, so as to prevent entrance of the foreign matter into the starter housing. Another proposed technique is the seal type pinion in which the pinion shaft has an enlarged circumference portion enough to close the diameter of the hole, as shown in FIG. 3.
Referring to FIG. 2, the dust food 25 is provided to encircle the flywheel 2 with the cooling fan 2 and has a hole 25A located just opposite the pinion 14 so that the pinion can enter the crankcase for engagement with the flywheel ring gear. This food 25 is very effective to prevent entrance of the foreign matter such as dust and debris into the starter housing 7.
However, because of the location of the cooling fan 2 in the vicinity of the hole 25A, dust through the fan 2 is allowed to enter the space 26, and eventually into the starter housing 7, when the fan is in operation.
This disadvantage would be further aggravated in a vertical crankshaft internal combustion engine in which the hole 25A stands at the bottom of the crankcase end wall allowing dust and dirt through the cooling fan 2 to fall to deposit in the starter housing 7.
Furthermore, since the hood 25 has to be mounted to completely enclose the flywheel 3, the overall crankcase construction becomes complicated with a consequent increase in production costs. In addition, in order to minimize the entrance of foreign matter through the cooling fan 2, the hole 25A has to have as small a diameter as possible and has to be located as near the flywheel ring gear. Since the cooling fan 2, in turn, is required to have a large capacity so that its front diameter consequently becomes large. Thus, the flywheel 3 has a stepped configuration, as illustrated in the drawing, with a large diameter top portion, so that the air from the fan 2 is not directly oriented to the hole 25A. However, this design makes the fan cover 5 to extend a great distance above the flywheel 3, which makes it impossible to have a desired small engine construction.
In addition, the space L defined around the flywheel 3 below its top portion becomes greater as the axial length of the flywheel 3 gets larger, forming, in some instances, a large pool for a great amount of the foreign matter to deposit so that considerable labor and time are required to remove the collected foreign matter there.
The seal type pinion, as illustrated in FIG. 3, does not require any dust hood enclosing the flywheel such as stated above. A bearing metal 27 is inserted in fixed position in the bore in the starter housing 7 through which the pinion 14 is reciprocated into or out of engagement with the flywheel ring gear. The pinion 14, in turn, has an enlarged neck portion 14A whose external diameter is substantially the same as the inside diameter of the bearing metal 27. Further, the neck portion 14A is formed to have a long axial length enough to keep the pinion shaft in constant contact at the external surface of the neck portion 14A with the bearing metal 27 while the pinion 14 is moved on the forward or backward stroke relative to the flywheel 3 ring gear. Since the bore is always closed in this manner, entrance of foreign matter into the starter motor 10 from inside the fan cover 5 is prevented.
However, this design puts to the pinion shaft an additional length for the neck portion 14A, which offers the disadvantage that the overall starter construction has an attendant increase in the axial length. Thus, these seal type pinion not only fails to meet the need for compact construction, desired for small general purpose engines, but also might pose a rigidity problem in the structure since the added length of the starter housing makes the crankcase have an increased overhang or downwardly extending distance as measured from the starter motor lower end to the attaching point, largely indicated at 8, of the starter housing to the crankcase 1.
It is these problems that gave rise to the present invention.